Shield structure and filament mount for electron discharge devices



Aug. 4, 1953 D. R. SHIELD STRUCTUR FOR ELECTRON DISCHARGE DEVICES KERSTETTER E AND FILAMENT MOUNT Filed Sept. 12, 1950 INVENTOR DONALD R.KER$TET TER .izw/

ATTORN Fatenteci Aug. 4, 1953 SHIELD STRUCTURE AND FILAMENT MOUNT FOR ELECTRON DISCHARGE DEVICES Donald R. Kerstetter, Emporium,.Pa., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application September 12, 1950, Serial No. 184,398

7 Claims. (Cl. 313-241) The present invention relates to electron discharge devices and more particularly to an improvement in the mount assembly of such devices.

An object of the present invention is a simplification of the construction of an electron discharge device.

Another object of the present invention is the provision of a unitary mount structure for filamentary type electron discharge devices.

Another object of the present invention is the provision of a mount structure for filamentary type electron discharge devices characterized by an improved filament anchoring structure.

Still another object of the present invention is the reduction of microphonic effects in electron discharge devices.

The foregoing objects and others which may appear from the following detailed description are attained in accordance with one aspect of the present invention as applied, for example, to an internally shielded high-frequency pentode amplifier tube by providing a support at the bottom of the mount structure and attached to the bottom shield for said mount to which the bot- .tom end of the filamentary cathode may be secured. The top end of the filamentary cathode is attached through the intermediary of a resilient spring to one of the other elements of the mount of the electron discharge device. Thus the advantages of a unitary mount structure as employed for indirectly heated cathode tubes may be obtained with filamentary cathode tubes.

Heretofore, as far as I am aware, it has been common practice to secure the bottom tab of the filament either directly to a pin or lead in wire passing through or sealed into the glass base of the tube or to an extension wire or bracket secured thereto.

With this form of construction it is apparent that the mount structure may be completely assembled except for the filament before the mount is secured to the leads coming through the glass base. The filament can only be inserted and connected after the mount is secured to the leadin conductors. Since the space between the bottom of the mount and the glass base is quite small, particularly in the case of miniature or sub-miniature tubes, it is extremely diflicult to satisfactorily make the weld between the bottom filament tab and its securing means and for the operator to properly adjust the position of the filament in the bottom insulating mica spacer formin part of the mount. Furthermore. in such previous forms of construction, especially in small sizes of tubes, when the glass base is sealed to the envelope of the tube the glass base may soften to some extent whereby the filament tension causes the pin to which the filament is attached to move slightly. This may disarrange the regularity of the arrangement of the pins in the pin circle or destroy the carefully predetermined filament tension.

Where the filament is, as in accordance with the present invention, secured at its bottom end to a tab either integral with or stamped out of the bottom shielding disc the filament may be inserted and adjusted as to tension before the mount is assembled to the header. Since the filament tension is not directly applied to any part which is anchored in glass, any slight softening of the glass will not be so likely to disarrange the pins in the circle nor upset the predetermined filament tension. Furthermore, since in my improved form of construction, one end of the filament is connected to the shieldin structure and the other to a suppressor grid structure, a lesser number of welds between the mount structure and the header pins is required.

While the invention is particularly applicable to filamentary type tubes the same mounting structure may be used for securing in place the cathode sleeve of an indirectly heated cathode type of tube. Thus the cathode is rigidly secured in position without the use of a beaded cathode sleeve. Due to the fact that the cathode sleeve is more rigidly held in position microphonic effects of the tube are decreased.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which Figure 1 illustrates in longitudinal section an electrical discharge tube utilizing an embodiment of the present invention while Figure 2 illustrates in perspective the bottom filament anchoring arrangement used in Figure 1.

In Figure 1 there is shown a filamentary type high-frequency pentode amplifier tube including an evacuated glass envelope l0 closed at one end by a glass header 1 2 through which are sealed a number of socket connection pins l4. Within the evacuated envelope I0 is arranged a mount, indicated generally at I5, which includes a pair of spaced perforated mica spacing discs l6 and I1 between which are attached in concentric interfitting arrangement an outermetal shield member IS, a hollow, generally cylindrical anode 20, a suppressor grid 22, a screen grid 24, a control grid 26 and a filamentary cathode 28. Each of the grids are generally similar in construction comprising a pair of side rods 30 and an open helical winding of grid lateral wire 3| secured to the side rods, usually by being swedged into notches on the outer edges of the side rods. The grids may be generally circular or elliptical in transverse sectional view. The pitch of the grid lateral wire winding 3| and the diameter of the grids may differ between the different grids in accordance with the functions which the grids are to perform.

In order to shield the structure from external electrical influences as much as possible, the mount is electrostatically closed at the top and bottom by metal shielding plates 32 and 34 lying against the outer faces of the spacer washers l6 and IT. A clearance hole such as that shown at 35 is provided in each of the shielding plates through which the cathode and the side rods of the grids protrude. The shielding plates are secured to the outer cage l by tabs such as that indicated at 36 extending through the spacing washers l6 and H and secured to the shield plates 32 and 34. They may be welded to lugs such as 34 or may be bent over against the outer faces of plates 32 and 34. The top end of filament 28 is connected by tab 38 to a resilient tension spring 40 attached through the intermediary of an interponent 42 to one of the side rods 30 of the suppressor grid 22. The tension applied to filament 28 by spring 40 may be adjusted during assembly by bending interponent 42. The other end of side rod 30 is connected to one of the lead-through or base pins l4.

In accordance with the present invention the bottom end of the filamentary cathode 28 is secured by interponent finger 46 to a tab 44 struck out of the material of shielding plate 34 or if desired, riveted or otherwise secured to said plate. In order to facilitate attachment of filament 28 to finger 4B the bottom end of the filament may be provided-with tab 38 similar to tab 38 at the other end of the filament. The shielding assembly composed of outer cylindrical cage 15 and plates 32 and 34 is electrically connected to one of the pins 14 extending through the header (2 by means of a short connection tab 48 as shown in Figure 1. Appropriate further connection leads are welded between side rods of the remaining grids, a tab on anode 20 and appropriate pins I4, but since such details of the construction of thetube do not, directly enter into the present invention but follows conventional practice, it is not believed necessary to describe them in further detail.

Hitherto known tubes generally of the type just described with which I am familiar, utilize separate connections for at least one end of the filament and for the shielding construction and/or the suppressor grid. In the present construction it will be noted that the filament is effectively connected in series between the suppressor grid and the shielding structure. However, since ordinarily, filamentary type tubes are designed to be operated at voltages of the order of one and one-half volts the resultant potential difierence between the suppressor grid electrode and shield, which is effectively at a zero reference potential, does not adversely affeet the operation of the tube.

Where the present form of construction is employed in vacuum tubes having indirectly heated cathodes using a hollow, tubular cathode with a heater element within the tubular cathode, the tubular cathode may be directly welded to hot- 4 tom tab 44, thus holding the cathode very rigidly in position without the necessity of employing a head on the sleeve resting against the mica washers l6 and I! to prevent longitudinal movement of the cathode sleeve.

While I have shown and particularly described an embodiment of the present invention it should be clearly understood that my invention is not limited thereto but that modifications and alterations within the scope of the invention may be made.

What I claim is:

1. An electron discharge device having, within an evacuated envelope, a mount including an anode, a filamentary cathode and a number of interposed grids, a shield plate at one end of said mount, an aperture in said shield plate, a bracket secured to said shield plate alongside said aperture and said cathode being connected at one end to said bracket.

2. An electron discharge device having, within an evacuated envelope, a mount including an anode, a filamentary cathode and a number of interposed grids, a shield plate at one end of said mount, an aperture in said shield plate, a bracket secured to said shield plate alongside said aperture and said cathode being connected at one end to said bracket and at the other end to a tensioning spring carried by another element of said mount.

3. A mount for an electron discharge device including a hollow shield cage electrostatically closed at each end by shielding plates, a filamentary cathode and at least one other electrode within said shield cage, one of said shielding plates having an aperture. a metal tab projecting outwardly of said hollow cage from said apertured shield plate and adjacent to said aperture, said filamentary cathode passing through said aperture and being anchored to said tab.

4. A mount for an electron discharge device including a hollow shield cage, insulating supporting means at each end of said cage, an anode and a grid within said shield cage and supported therein by said insulating means, an apertured shield plate over one of said insulating means, a tab connected to said shield plate adjacent said aperture and extending away from said mount in a direction generally perpendicular to said shield plate, and a filamentary cathode passing through said insulating supporting means and said cage and connected at one end to said tab and at the other end to said grid electrode.

5. An electron discharge device having, within an evacuated envelope, a mount containing electrodes including an anode, a filamentary cathode, and a number of interposed grids, said anode and grids being provided with projecting portions for mounting, a pair of insulating spacer members included in said mount and adapted to receive and retain said projecting portions of said electrodes so as to maintain a predetermined, spaced relation between them, said mount including a hollow shield cage electrostatically closed at each end by shielding plates, said shielding plates being provided with suitable apertures to pass said projecting portions without electrical contact, one of said shielding plates having a tab projecting outwardly of said mount and located adjacent said aperture, one end of said cathode being anchored to said projecting 6. An electron discharge device having, within an evacuated envelope, a mount containing electrodes including an anode, a filamentary cathode, and a number of interposed grids, said anode and grids being provided with projecting portions for mounting, a pair of insulating spacer members included in said mount and adapted to receive and retain said projecting portions of said electrodes so as to maintain a predetermined, spaced relation between them, said mount including a hollow shield cage electrostatically closed at each end by shielding plates, said shielding plates being provided with suitable apertures to pass said projecting portions without electrical contact, one of said shielding plates having a tab formed by striking and bending outwardly a portion of the material of said plate so as to contribute to the formation of said aperture, one end of said cathode being anchored to said projecting tab.

7. An electron discharge device having, within an evacuated envelope, a mount containing electrodes including an anode, a filamentary cathode, and a number of interposed grids, said anode and grids being provided with projecting portions for mounting, a pair of insulating spacer members included in said mount and adapted to receive and retain said projecting portions of said electrodes as to maintain a predetermined, spaced relation between them, said mount including a hollow shield cage electrostatically closed at each end by shielding plates, said shielding plates being provided with suitable apertures to pass said projecting portions without electrical contact, one of said shielding plates having a tab formed by striking and bending outwardly a portion of the material of said plate so as to contribute to the formation of said aperture, one end of said cathode being anchored to said projecting tab by means of a resilient member attached to the outer end of said tab and extending therefrom towards said mount and away from said tab.

DONALD R. KERSTEI'TER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,040,267 Orth May 12, 1936 2,355,083 Krim Aug. 8, 1944 2,572,032 Jacobus et al Oct. 23, 1951 

